Palladium-catalyzed C-H glycosylation and retro Diels-Alder tandem reaction via structurally modified norbornadienes (smNBDs)

This report describes palladium-catalyzed C–H glycosylation and retro Diels–Alder tandem reaction via structurally modified norbornadienes (smNBDs). smNBDs were proposed to regulate the reactivity of the aryl-norbornadiene-palladacycle (ANP), including its high chemoselectivity and regioselectivity, which were the key to constructing C2 and C3 unsubstituted C4-glycosidic indoles. The scope of this substrate is extensive; the halogenated six-membered and five-membered glycosides were applied to the reaction smoothly, and N-alkyl (primary, secondary and tertiary) C4-glycosidic indoles can also be obtained by this method. In terms of mechanism, the key ANP intermediates characterized by X-ray single-crystal diffraction and further controlled experiments proved that the migration-insertion of smNBDs with phenylpalladium intermediate endows them with high chemo- and regioselectivity. Finally, density functional theory (DFT) calculation further verified the rationality of the mechanism.

This report describes palladium-catalyzed C–H glycosylation and retro Diels–Alder tandem reaction via structurally modified norbornadienes (smNBDs).

Palladium/norbornene-catalyzed distal alkenyl C-H arylation and alkylation of cis-olefins

In this full article, a detailed study of a distal alkenyl C-H arylation and alkylation through the palladium/norbornene (NBE) cooperative catalysis is described. Both aminopyridine- and oxime ether-type directing groups have been found effective for this transformation, allowing functionalization of diverse allyl amines and homoallyl alcohols. In addition, the C5,C6-substititued NBEs show optimal reactivity and selectivity. Various cis-olefins can be transformed to the corresponding arylated or alkylated trisubstituted alkenes with excellent regio- and stereoselectivity. Preliminary mechanistic studies support the Catellani pathway instead of the Heck pathway.

C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates

In this review article, we summarized recent advances in C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates.

Distal Alkenyl C-H Functionalization via the Palladium/Norbornene Cooperative Catalysis

A distal-selective alkenyl C-H arylation method is reported through a directed palladium/norbornene (Pd/NBE) cooperative catalysis. The key is to use an appropriate combination of the directing group and the NBE cocatalyst. A range of acyclic and cyclic cis-olefins are suitable substrates, and the reaction is operated under air with excellent site-selectivity. Preliminary mechanistic studies are consistent with the proposed Pd/NBE-catalyzed C-H activation instead of the Heck pathway. Initial success on distal alkylation has also been achieved using MeI and methyl bromoacetate as electrophiles.

Pd/NBE-catalyzed sequential carbamoylation/olefination of aryl iodides

We present a Pd/NBE-catalyzed sequential carbamoylation/olefination of aryl iodides under mild reaction conditions, which provide diverse 4-methylene-3,4-dihydro-1(2H)-isoquinolin-1-one analogues.

Palladium/Norbornene Cooperative Catalysis

Palladium/norbornene cooperative catalysis has emerged as a distinct approach to construct polyfunctionalized arenes from readily available starting materials. This Review provides a comprehensive overview of this field, including the early stoichiometric investigations, catalytic reaction developments, as well as the applications in the syntheses of bioactive compounds and polymers. The section of catalytic reactions is divided into two parts according to the reaction initiation mode: Pd(0)-initiated reactions and Pd(II)-initiated reactions.

Temperature-controlled sequential Suzuki-Miyaura reactions for preparing unsymmetrical terphenyls

A one-pot protocol of double Suzuki-Miyaura reactions has been developed for the synthesis of unsymmetrical terphenyls. In the absence of a ligand, potassium bromophenyltrifluoroborate reacts with arylboronic acid and then sequentially with a hetero/aryl bromide by controlling the reaction temperature, providing unsymmetrical p- and m-terphenyl compounds in moderate to good overall yields. This protocol provides a convenient and practical approach to unsymmetrical terphenyls under ligand-free and aerobic conditions.

Expeditious Synthesis of 6-Fluoroalkyl-Phenanthridines via Palladium-Catalyzed Norbornene-Mediated Dehydrogenative Annulation

A novel palladium-catalyzed, norbornene-mediated intermolecular dehydrogenative annulation approach for the synthesis of 6-fluoroalkyl-phenanthridines from aryl iodides and fluorinated imidoyl chlorides, which are important structural motifs for bioactive molecules, is reported. Fluorinated imidoyl chlorides served as a new type of electrophilic reagent in the Catellani-type reaction, which, in turn, could be readily prepared from various anilines and fluorinated carboxylic acids. Control experiments were carried out to study the mechanism of the reaction. This transformation is scalable and tolerates a broad range of functional groups.

Suzuki-Miyaura Coupling of Simple Ketones via Activation of Unstrained Carbon-Carbon Bonds

Here, we describe that simple ketones can be efficiently employed as electrophiles in Suzuki-Miyaura coupling reactions via catalytic activation of unstrained C-C bonds. A range of common ketones, such as cyclopentanones, acetophenones, acetone and 1-indanones, could be directly coupled with various arylboronates in high site-selectivity, which offers a distinct entry to more functionalized aromatic ketones. Preliminary mechanistic study suggests that the ketone α-C-C bond was cleaved via oxidative addition.

Palladium-Catalyzed Arylation of Ketones and Acetonitrile with Ortho Alkylation of Aryl Rings: De Novo Synthesis of Tetralines and Benzocycloheptenes

Palladium-catalyzed α-arylation reactions of ketones with simultaneous ortho alkylation offer 1,2,3-substituted arenes. The reactions of 1,ω-dihaloalkanes also allow facile construction of medicinally important tetralines and benzocycloheptenes.

Pd-catalyzed dehydrogenative annulation approach for the efficient synthesis of phenanthridinones

A novel Pd-catalyzed intermolecular dehydrogenative annulation of aryl iodides and aryl carbamic chlorides for the efficient synthesis of phenanthridinone derivatives was developed. Simple aryl iodides and carbamic chlorides readily made from various anilines, a broad substrate scope with hetero/polycycles, as well as high-value products, make this direct dehydrogenative annulation approach very practical and attractive.

Highly regioselective meta arylation of oxalyl amide-protected β-arylethylamine via the Catellani reaction

A first bidentate directing group assisted highly selective meta arylation of β-arylethylamine derivatives with various iodides is reported.

Pd-catalyzed one-pot sequential unsymmetrical cross-coupling reactions of aryl/heteroaryl 1,2-dihalides

The present methodology allows the conversion of easily available aryl/heteroaryl 1,2-dihalides into synthetically useful unsymmetrically substituted arenes/heteroarenes in good to excellent yields under mild reaction conditions.

Ortho C-H Acylation of Aryl Iodides by Palladium/Norbornene Catalysis

Reported herein is a palladium/norbornene-catalyzed ortho-arene acylation of aryl iodides by a Catellani-type C-H functionalization. This transformation is enabled by isopropyl carbonate anhydrides, which serve as both an acyl cation equivalent and a hydride source.

Palladium-catalyzed dearomative cyclization by a norbornene-mediated sequence: a route to spiroindolenine derivatives

Spiroindolenine derivatives bearing an all-carbon quaternary spirocenter are synthesizedviaa Pd-catalyzed norbornene-mediated tandemortho-alkylation dearomative cyclization reaction.

Palladium/norbornene chemistry: an unexpected route to methanocarbazole derivatives via three Csp3–Csp2/Csp3–N/Csp2–N bond formations in a single synthetic sequence

A simple route to obtain fused indolinesviaa palladium-catalyzed norbornene-mediated Heck reaction/C–H activation/double amination cascade is described.

Palladium-catalyzed cascade C-H trifluoroethylation of aryl iodides and Heck reaction: efficient synthesis of ortho-trifluoroethylstyrenes

A palladium-catalyzed selective C-H bond trifluoroethylation of aryl iodides has been explored. The reaction allows for the efficient synthesis of a variety of ortho-trifluoroethyl-substituted styrenes. Preliminary mechanistic studies indicate that the reaction might involve a key Pd(IV) intermediate, which is generated through the rate-determining oxidative addition of CF3CH2I to a palladacycle; the bulky nature of CF3CH2I influences the reactivity. Reductive elimination from the Pd(IV) complex then leads to the formation of the aryl-CH2CF3 bond.

Of the ortho effect in palladium/norbornene-catalyzed reactions: a theoretical investigation

Mechanistic questions concerning palladium and norbornene catalyzed aryl-aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the "ortho effect" (caused by an ortho substituent in the starting aryl halide), which leads to aryl-aryl coupling with a second molecule of aryl halide rather than to aryl-norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading to Pd(IV). The unselective sp(2)-sp(2) and sp(2)-sp(3) coupling, experimentally observed in this case, can be explained in the framework of the transmetalation pathway since the energetic difference between aryl attack onto the aryl or norbornyl carbon of the palladacycle intermediate is quite small. On the other hand, according to the experimentally observed "ortho effect", selective aryl-aryl coupling only occurs in the reactions of ortho-substituted metallacycles. The present work offers the first possible rationalization of this finding. These in situ formed palladacycles containing an ortho substituent could more easily undergo oxidative addition of an aryl halide rather than reductive elimination from the transmetalation intermediate as a result of a steric clash in the transition state of the latter. The now energetically accessible Pd(IV) intermediate, featuring a Y-distorted trigonal bipyramidal structure, can account for the reported selective aryl-aryl coupling through a reductive elimination which is easier than aryl-norbornyl coupling. Thus, the steric effect represents the main factor that dictates the energetic convenience of the system to follow the Pd(IV) or the transmetalation pathway. Ortho substituents cause a higher energy transition state for reductive elimination from the transmetalation intermediate than for oxidative addition to the metallacycle palladium(II) and the pathway based on the latter predominates.